Paul,
Can you describe your water catchment system? Any filters used before flowing into the tank or before cooking/drinking? I think in this era of technology and industrialized conveniences we often forget that drinking water falls from the sky.

I have two water tanks: rinse water and drinking water. The rinse-water tank has a deck-fill by the rail. When it rains, I plug the scupper in front of the deck fill and put a dam behind it. The plug and dam are made from butyl rubber "tape." Between the tank and the sinks is a sediment filter. I catch drinking water in buckets either from a canvass tarp draped over the boom, or from the rolled-up genoa (in a bucket under the roller furler). I then manually fill the tank from the buckets. Rainwater is completely pure, assuming it falls through clean air. It's technically the same as distilled water. But it can pick up substances from the tarp, or the sail, or the plastic buckets and tank, so I use the charcoal filter. I don't expect we have any air pollution here in Bocas del Toro. It would be different near a city or industry.